1. Field of the Invention
This invention relates to novel synthetic lubricating oils which are particularly excellent in oxidation resistance and contain as the main component at least one member selected from specified naphthoic acid esters, naphthyl ethers and naphthol esters, and it also relates to the novel specified naphthoic acid esters and naphthyl ethers for use in the novel synthetic lubricating oils.
2. Description of the Prior Art
Lubricating oils are generally required to have a long-term service life. To meet this requirement, a highly refined mineral oil to which a suitable antioxidant has been added as required, is used as a lubricating oil. The mineral oil, however, has limited oxidation resistance and is therefore difficult to use for a long period of time under severe circumstances. Thus, ester-based synthetic oils such as diesters and polyol esters as well as hydrocarbon synthetic oils such as .beta.-olefins, have been developed and now widely used as lubricating oils having excellent oxidation stability.
These hitherto-known synthetic lubricating oils are deemed to have higher oxidation stability than the mineral oils, but their oxidation stability is not fully satisfactory.